Liquid crystal display

ABSTRACT

A thin film transistor array panel is provided, which includes: a substrate; a plurality of first signal lines formed on the substrate; a plurality of second signal lines intersecting the first signal lines to define pixel areas; first and second pixel electrodes disposed substantially in a pixel area and having different areas; a plurality of thin film transistors connected to the first and the second signal lines and at least one of the first and the second pixel electrodes; a coupling electrode overlapping the second pixel electrode; and a tilt direction defining member for determining tilt directions of liquid crystal molecules formed on the substrate.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. application Ser. No.12/369,260 filed on Feb. 11, 2009 now U.S. Pat. No. 7,852,442, which isa continuation of U.S. patent application Ser. No. 11/566,496 filed Dec.4, 2006, now U.S. Pat. No. 7,495,735 which is a continuation of Ser. No.10/866,536 filed Jun. 10, 2004, now U.S. Pat. No. 7,158,201 which claimspriority to Korean Application No. 2003-37090 filed Jun. 10, 2003, theentireties of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

(a) Field of the Invention

The present invention relates to a liquid crystal display.

(b) Description of the Related Art

A liquid crystal display (LCD) is one of the most widely used flat paneldisplays. An LCD includes two panels provided with field-generatingelectrodes such as pixel electrodes and a common electrode and a liquidcrystal (LC) layer interposed therebetween. The LCD displays images byapplying voltages to the field-generating electrodes to generate anelectric field in the LC layer, which determines orientations of LCmolecules in the LC layer to adjust polarization of incident light.

Among the LCDs, a vertical alignment (VA) mode LCD, which aligns LCmolecules such that the long axes of the LC molecules are perpendicularto the panels in absence of electric field, is spotlighted because ofits high contrast ratio and wide viewing angle.

The wide viewing angle of the VA mode LCD can be realized by cutouts inthe field-generating electrodes and protrusions on the field-generatingelectrodes. Since the cutouts and the protrusions can determine the tiltdirections of the LC molecules, the tilt directions can be distributedinto several directions by using the cutouts and the protrusions suchthat the viewing angle is widened.

However, the VA mode LCD has relatively poor lateral visibility comparedwith front visibility.

SUMMARY OF THE INVENTION

A thin film transistor array panel is provided, which includes: asubstrate; a plurality of first signal lines formed on the substrate; aplurality of second signal lines intersecting the first signal lines todefine pixel areas; first and second pixel electrodes disposedsubstantially in a pixel area and having different areas; a plurality ofthin film transistors connected to the first and the second signal linesand at least one of the first and the second pixel electrodes; acoupling electrode overlapping the second pixel electrode; and a tiltdirection defining member for determining tilt directions of liquidcrystal molecules formed on the substrate.

A liquid crystal display is provided, which includes: a thin filmtransistor array panel, a common electrode panel, a first tilt directiondefining member formed on the thin film transistor array panel, and asecond tilt direction defining member determining tilt directions ofliquid crystal molecules along with the first tilt direction definingmember formed on the common electrode panel. The thin film transistorarray panel includes: a plurality of first signal lines; a plurality ofsecond signal lines intersecting the first signal lines to define pixelareas; first and second pixel electrodes disposed substantially in apixel area and having different areas; a plurality of thin filmtransistors connected to the first and the second signal lines and atleast one of the first and the second pixel electrodes; and a couplingelectrode overlapping the second pixel electrode. The common electrodepanel includes a common electrode for generating an electric field alongwith the first and the second pixel electrodes;

The first and the second tilt direction defining members may includecutouts formed in the pixel electrodes and the common electrode.

The liquid crystal display is provided, which includes: a firstsubstrate; a plurality of first signal lines formed on the firstsubstrate; a plurality of second signal lines intersecting the firstsignal lines to define pixel areas; first and second pixel electrodesdisposed substantially in a pixel area; a plurality of thin filmtransistors connected to the first and the second signal lines and atleast one of the first and the second pixel electrodes; a couplingelectrode overlapping the second pixel electrode; a second substratefacing the first substrate; a common electrode formed on the secondsubstrate; a first tilt direction defining member formed on the thinfilm transistor array panel; and a second tilt direction defining memberdetermining tilt directions of liquid crystal molecules along with thefirst tilt direction defining member formed on the common electrodepanel, wherein a ratio of a voltage difference between the first pixelelectrode and the common electrode and a voltage difference between thesecond pixel electrode and the common electrode is in a range betweenabout 0.5-0.95.

The tilt direction determining member may include a cutout of one of thefirst and the second pixel electrodes.

The coupling electrode may be connected to a drain electrode of one ofthe thin film transistors.

The first and the second pixel electrodes may have edges facing eachother and forming a gap and the gap includes oblique portions making anangle of about 45 degrees with the gate lines.

The thin film transistor array panel may further include a third signalline intersecting the second signal lines and supplied with a referencevoltage, wherein the first and the second pixel electrodes arecapacitively coupled to each other through the coupling electrode, andthe thin film transistors comprise a first transistor connected to oneof the first signal lines, one of the second signal lines, and the firstpixel electrode and a second transistor connected to one of the firstsignal lines, the third signal line, and the second pixel electrode.

The thin film transistor array panel may further include an insulatinglayer disposed between the first and the second pixel electrodes and thefirst and the second transistors and having a first contact hole forconnecting the second pixel electrode to the second transistor.

The thin film transistor array panel may further include an insulatinglayer disposed between the first and the second pixel electrodes and thefirst and the second transistors, wherein the first pixel electrode isconnected to the first transistor or overlaps a drain electrode of thefirst transistor.

The first pixel electrode may have an area larger than the second pixelelectrode.

The first pixel electrode may have an area once to six times an area ofthe second pixel electrode.

The thin film transistor array panel may further include a third pixelelectrode capacitively coupled to the first pixel electrode.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more apparent by describingembodiments thereof in detail with reference to the accompanyingdrawings in which:

FIG. 1 is a layout view of a TFT array panel of an LCD according to anembodiment of the present invention;

FIG. 2 is a layout view of a common electrode panel of an LCD accordingto an embodiment of the present invention;

FIG. 3 is a layout view of an LCD including the TFT array panel shown inFIG. 1 and the common electrode panel shown in FIG. 2;

FIG. 4 is a sectional view of the LCD shown in FIG. 4 taken along theline V-V′;

FIG. 5 is an equivalent circuit of the LCD shown in FIGS. 1-4;

FIG. 6 is a layout view of a TFT array panel for an LCD according toanother embodiment of the present invention;

FIG. 7 is an equivalent circuit diagram of an LCD including the TFTarray panel shown in FIG. 6;

FIG. 8 is a layout view of a TFT array panel for an LCD according toanother embodiment of the present invention;

FIG. 9 is an equivalent circuit diagram of an LCD including the TFTarray panel shown in FIG. 8;

FIG. 10 is a layout view of a TFT array panel for an LCD according toanother embodiment of the present invention;

FIG. 11 is an equivalent circuit diagram of an LCD including the TFTarray panel shown in FIG. 10; and

FIGS. 12 and 13 are layout views of TFT array panels for an LCDaccording to another embodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

The present invention now will be described more fully hereinafter withreference to the accompanying drawings, in which preferred embodimentsof the invention are shown. The present invention may, however, beembodied in many different forms and should not be construed as limitedto the embodiments set forth herein.

In the drawings, the thickness of layers, films and regions areexaggerated for clarity. Like numerals refer to like elementsthroughout. It will be understood that when an element such as a layer,film, region or substrate is referred to as being “on” another element,it can be directly on the other element or intervening elements may alsobe present. In contrast, when an element is referred to as being“directly on” another element, there are no intervening elementspresent.

Now, liquid crystal displays and thin film transistor (TFT) array panelsfor LCDs according to embodiments of the present invention will bedescribed with reference to the accompanying drawings.

An LCD according to an embodiment of the present invention will bedescribed in detail with reference to FIGS. 1-5.

FIG. 1 is a layout view of a TFT array panel of an LCD according to anembodiment of the present invention, FIG. 2 is a layout view of a commonelectrode panel of an LCD according to an embodiment of the presentinvention, FIG. 3 is a layout view of an LCD including the TFT arraypanel shown in FIG. 1 and the common electrode panel shown in FIG. 2,and FIG. 4 is a sectional view of the LCD shown in FIG. 4 taken alongthe line V-V′.

An LCD according to an embodiment of the present invention includes aTFT array panel 100, a common electrode panel 200, and a LC layer 300interposed between the panels 100 and 200 and containing a plurality ofLC molecules 310 aligned substantially vertical to surfaces of thepanels 100 and 200.

The TFT array panel 100 is now described in detail with reference FIGS.1, 3 and 4.

A plurality of gate lines 121 and a plurality of storage electrode lines131 are formed on an insulating substrate 110 such as transparent glass.

The gate lines 121 extend substantially in a transverse direction andare separated from each other and transmit gate signals. Each gate line121 includes a plurality of first and second gate electrodes 123 a and123 b and an end portion 125 having a large area for connection with anexternal driving circuit. The first gate electrode 123 a has a widthwider than other portions of the gate line 121.

Each storage electrode line 131 extends substantially in the transversedirection and includes a plurality of ring-shaped branches 133 a-133 cand a plurality of branch connections 133 d connected between adjacentbranches 133 a-133 c. Each branch set includes a pair of first andsecond storage electrodes 133 a and 133 b extending in a longitudinaldirection and a third storage electrode 133 c connected to ends of thefirst and the second storage electrodes 133 a and 133 b and extending inthe transverse direction and in an oblique direction. The storageelectrode lines 131 are supplied with a predetermined voltage such as acommon voltage, which is applied to a common electrode 270 on the commonelectrode panel 200 of the LCD. The third storage electrodes 133 c maybe connected to each other.

The gate lines 121 and the storage electrode lines 131 is preferablymade of Al containing metal such as Al and Al alloy, Ag containing metalsuch as Ag and Ag alloy, Cu containing metal such as Cu and Cu alloy, Mocontaining metal such as Mo and Mo alloy, Cr, Ti or Ta. The gate lines121 and the storage electrode lines 131 may have a multi-layeredstructure including two films having different physical characteristics,a lower film (not shown) and an upper film (not shown). The upper filmis preferably made of low resistivity metal including Al containingmetal such as Al and Al alloy for reducing signal delay or voltage dropin the gate lines 121 and the storage electrode lines 131. On the otherhand, the lower film is preferably made of material such as Cr, Mo andMo alloy, which has good contact characteristics with other materialssuch as indium tin oxide (ITO) or indium zinc oxide (IZO). However, thegate lines 121 and the storage electrode lines 131 may be made of othervarious metals or conductive materials.

In addition, the lateral sides of the gate lines 121 and the storageelectrode lines 131 are inclined relative to a surface of the substrate,and the inclination angle thereof ranges about 20-80 degrees.

A gate insulating layer 140 preferably made of silicon nitride (SiNx) isformed on the gate lines 121 and the storage electrode lines 131.

A plurality of semiconductor stripes 151 and a plurality ofsemiconductor islands 154 b preferably made of hydrogenated amorphoussilicon (abbreviated to “a-Si”) or polysilicon are formed on the gateinsulating layer 140. Each semiconductor stripe 151 extendssubstantially in the longitudinal direction and has a plurality ofprojections 154 a branched out toward the first gate electrodes 123 a.The semiconductor islands 154 b are disposed on the second gateelectrodes 123 b.

A plurality of ohmic contact stripes and islands 161 and 165 a as wellas a plurality of ohmic contact islands (not shown), which arepreferably made of silicide or n+ hydrogenated a-Si heavily doped with ntype impurity such as phosphorous, are formed on the semiconductorstripes 151 as well as on the semiconductor islands 154 b. Each ohmiccontact stripe 161 has a plurality of projections 163, and theprojections 163 and the ohmic contact islands 165 are located in pairson the projections 154 a of the semiconductor stripes 151. The ohmiccontact islands on the semiconductor islands 154 b are also located inpairs.

The lateral sides of the semiconductor stripes 151 and the ohmiccontacts 161 and 165 are inclined relative to a surface of thesubstrate, and the inclination angles thereof are preferably in a rangebetween about 30-80 degrees.

A plurality of data lines 171 including a plurality of first sourceelectrodes 173 a and a plurality of first drain electrodes 175 a as wellas a plurality of second source electrodes 173 b and a plurality ofsecond drain electrodes 175 b are formed on the ohmic contacts 161 and165 and the gate insulating layer 140 as well as on the semiconductorislands 154 b.

The data lines 171 for transmitting data voltages extend substantiallyin the longitudinal direction and intersect the gate lines 121, thestorage electrode lines 131, and the branch connections 133 d. Each dataline 171 is disposed between adjacent branches 133 a-133 c and itincludes an end portion 179 having a large area for contact with anotherlayer or an external device. A plurality of branches of each data line171, which project toward the first drain electrodes 175 a, form thefirst source electrodes 173 a. The second source electrodes 173 b andthe second drain electrodes 175 b are disposed on the second gateelectrodes 123 b. Each of the first/second drain electrodes 175 a/175 bextends upward/downward from an end portion and includes an expansionhaving a large area for contact with another layer and each of thefirst/second source electrodes 173 a/173 b is curved to partly enclosean end portion of the first/second drain electrode 175 a/175 b.

A first gate electrode 123 a, a first source electrode 173 a, and afirst drain electrode 175 a along with a projection 154 a of asemiconductor stripe 151 form a first TFT having a channel formed in theprojection 154 a disposed between the first source electrode 173 a andthe first drain electrode 175 a. Similarly, a second gate electrode 123b, a second source electrode 173 b, and a second drain electrode 175 balong with a semiconductor island 154 b form a second TFT having achannel formed in the semiconductor island 154 b disposed between thesecond source electrode 173 b and the second drain electrode 175 b.

In the meantime, each of the first drain electrodes 175 a extends toform a coupling electrode 176 b and the coupling electrode 176 bincludes a longitudinal portion partly overlapping a first storageelectrode 133 a, three oblique portions connected to the longitudinalportion and extending parallel to each other, and a transverse portionconnected to one of the three oblique portions and partly overlappingthe third storage electrode 133 c. The oblique portions of the couplingelectrode 176 b make an angle of about 45 degrees with the gate lines121. Two of the oblique portions are connected to respective ends of thelongitudinal portion and approximately making a right angle andremaining one of the oblique portions are connected to an intermediatepoint of the longitudinal portion and to the expansion of the firstdrain electrode 175 b.

The data lines 171, the drain electrodes 175 a and 175 b, and the secondsource electrodes 173 b are preferably made of refractory metal such asCr, Mo containing metal, Ti and Ti, or Al containing metal and they mayalso have a multilayered structure including a lower film (not shown)preferably made of refractory metal and an upper film (not shown)located thereon and preferably made of low resistivity material.

Like the gate lines 121 and the storage electrode lines 131, the datalines 171, the drain electrodes 175 a and 175 b, and the second sourceelectrodes 173 b have tapered lateral sides, and the inclination anglesthereof range about 30-80 degrees.

The ohmic contacts 161 and 165 are interposed only between theunderlying semiconductor stripes 151 and the overlying data lines 171,the overlying drain electrodes 175 a and 175 b, and the second sourceelectrodes 173 b thereon and reduce the contact resistance therebetween.The semiconductor stripes and islands 151 and 154 b include a pluralityof exposed portions, which are not covered with the data lines 171, thedrain electrodes 175 a and 175 b, and the second source electrodes 173b, such as portions located between the source electrodes 173 a and 173b and the drain electrodes 175 a and 175 b.

A passivation layer 180 is formed on the data lines 171, the drainelectrodes 175 a and 175 b, the second source electrodes, and theexposed portions of the semiconductor stripes 151. The passivation layer180 is preferably made of photosensitive organic material having a goodflatness characteristic, low dielectric insulating material havingdielectric constant lower than 4.0 such as a-Si:C:O and a-Si:O:F formedby plasma enhanced chemical vapor deposition (PECVD), or inorganicmaterial such as silicon nitride. The passivation layer 180 may includea lower film of inorganic insulator and an upper film of organicinsulator.

The passivation layer 180 has a plurality of contact holes 181 a, 181 b,183 and 186 exposing the expansions of the first and the second drainelectrodes 175 a and 175 b, the end portions 179 of the data lines 171,and the second source electrodes 173 b, respectively. The passivationlayer 180 and the gate insulating layer 140 have a plurality of contactholes 182, 183 and 184 exposing the end portions 125 of the gate lines121, end portions of the first storage electrodes 133 a, and portions ofthe storage electrode lines 131 near the end portions of the firststorage electrodes 133 a, respectively.

A plurality of pairs of first and second pixel electrodes 190 a and 190b, a plurality of contact assistants 95 and 97, and a plurality ofstorage connections 91, which are preferably made of a transparentconductor such as ITO and IZO or a reflective conductor such as Al, areformed on the passivation layer 180.

The storage connections 91 cross over the gate lines 121 and the secondsource electrodes 173 b and they are connected to the exposed projectionof the end portions of the first storage electrodes 133 a and theexposed portions of the storage electrode lines 131 respectively throughthe contact holes 184 and 185 opposite each other with respect to thegate lines 121. In addition, the storage connections 91 are connected tothe second source electrodes 173 b through the contact holes 186. Thestorage electrode lines 131 including the storage electrodes 133 a and133 b along with the storage connections 91 and the second source 173 bmay be used for repairing defects in the gate lines 121, the data lines171, or the TFTs. The electrical connection between the gate lines 121and the storage electrode lines 131 for repairing the gate lines 121 isobtained by illuminating the cross points of the gate lines 121 and thestorage connections 91 by a laser beam to electrically connect the gatelines 121 to the storage connections 91. In this case, the second sourceelectrodes 173 b enhance the electrical connection between the gatelines 121 and the storage connections 91.

The first/second pixel electrodes 190 a/190 b are physically andelectrically connected to the first/second drain electrodes 175 a/175 bthrough the contact holes 181 a/181 b such that the first/second pixelelectrodes 190 a/190 b receive the data/common voltages from thefirst/second drain electrodes 175 a/175 b. In addition, the second pixelelectrodes 190 b overlap the coupling electrodes 176 b.

The pixel electrodes 190 a and 190 b supplied with the data voltagesgenerate electric fields in cooperation with the common electrode 270,which reorient liquid crystal molecules 310 in the liquid crystal layer300.

A pixel electrode 190 a/190 b and the common electrode 270 form a liquidcrystal capacitor, which stores applied voltages after turn-off of theTFT. An additional capacitor called a “storage capacitor,” which isconnected in parallel to the liquid crystal capacitor, is provided forenhancing the voltage storing capacity. The storage capacitors areimplemented by overlapping the pixel electrodes 190 a and 190 b with thestorage electrode lines 131 including the storage electrodes 133 a, 133b and 133 c.

A pair of first and second pixel electrodes 190 a and 190 b engage witheach other interposing a gap 191 and their outer boundary hassubstantially a shape of rectangle with chamfered left corners. Thefirst pixel electrode 190 a has a shape of a rotated equilateraltrapezoid having a left edge disposed near a longitudinal portion of acoupling electrode 176 b, a right edge disposed near a second storageelectrode 133 b, and a pair of upper and lower oblique edges extendingsubstantially parallel to the oblique portions of the coupling electrode176 b and thereby making an angle of about 45 degrees with the gatelines 121. The second pixel electrode 190 b includes a pair oftrapezoidal portions facing the oblique edges of the first pixelelectrode 190 a and a longitudinal portion facing the left edge of thefirst pixel electrode 190 a. Accordingly, the gap 191 has a pair ofoblique upper and lower portions having a substantially uniform widthand making an angle of about 45 degrees with the gate lines 121 and alongitudinal portion having a substantially uniform width.

The first pixel electrode 190 a has upper and lower cutouts 192 and apair of middle cutouts 193 and 194, which partition the first pixelelectrode 190 a into a plurality of partitions. The upper and the lowercutouts 192 are disposed at upper and lower halves of the pixelelectrode 190, respectively, and the middle cutouts 193 and 194 arelocated between the upper cutout 92 and the lower cutout 92. The gap 191and the cutouts 192 and 194 substantially have inversion symmetry withrespect to an imaginary transverse center line bisecting the upper andthe lower halves of the first pixel electrode 190 a.

The upper cutout 192 extends substantially parallel to the upper obliqueportion of the gap 191 and substantially perpendicular to the lowercutout 192, which extends substantially parallel to the upper obliqueportion of the gap 191. The upper and the lower cutouts 192 extendapproximately from the left edge of the first pixel electrode 190 aapproximately to the right edge of the first pixel electrode 190 a.

The middle cutout 193 includes a transverse portion extendingapproximately from the left edge of the first pixel electrode 190 aalong the transverse center line of the pixel electrode 190 and a pairof oblique portions extending from the transverse portion to the rightedge of the first pixel electrode 190 a and extending substantiallyparallel to the upper cutout 192 and the lower cutout 192, respectively.The middle cutout 194 extends along the transverse center line of thefirst pixel electrode 190 a and has an inlet from the right edge of thepixel electrode 190, which has a pair of oblique edges substantiallyparallel to the upper cutout 192 and the lower cutout 192, respectively.

Accordingly, the upper half of the first pixel electrode 190 a is alsopartitioned into three upper partitions by the upper cutout 192 and themiddle cutout 193, and the lower half of the first pixel electrode 190 ais partitioned into three lower partitions by the lower cutout 192 andthe middle cutout 193. The number of partitions or the number of thecutouts is varied depending on the design factors such as the size ofpixels, the ratio of the transverse edges and the longitudinal edges ofthe first and second pixel electrodes 190 a and 190 b, the type andcharacteristics of the liquid crystal layer 300, and so on. Fordescriptive convenience, the gap 191 is also referred to as a cutout.

In the meantime, the storage electrode lines 131 may further include aplurality of branches (not shown) overlapping the cutouts 191-194.

The contact assistants 95 and 97 are connected to the end portions 125of the gate lines 121 and the end portions 179 of the data lines 171through the contact holes 182 and 183, respectively. The contactassistants 95 and 97 protect the end portions 125 and 179 and complementthe adhesiveness of the end portions 125 and 179 and external devices.

The description of the common electrode panel 200 follows with referenceto FIGS. 2-4.

A light blocking member 220 called a black matrix for preventing lightleakage is formed on an insulating substrate 210 such as transparentglass. The light blocking member 220 may include a plurality of openingsthat face the pixel electrodes 190 and it may have substantially thesame shape as the pixel electrodes 190.

A plurality of color filters 230 are formed on the substrate 210 andthey are disposed substantially in the areas enclosed by the lightblocking member 220. The color filters 230 may extend substantiallyalong the longitudinal direction along the pixel electrodes 190. Thecolor filters 230 may represent one of the primary colors such as red,green and blue colors.

An overcoat 250 for preventing the color filters 230 from being exposedand for providing a flat surface is formed on the color filters 230 andthe light blocking member 220.

A common electrode 270 preferably made of transparent conductivematerial such as ITO and IZO is formed on the overcoat 250.

The common electrode 270 has a plurality of sets of cutouts 271-276.

A set of cutouts 271-276 face a pair of first and second pixelelectrodes 190 a and 190 b and include a plurality of lower and uppercutouts 271 and 272 and 275 and 276 and middle cutouts 273 and 274. Eachof the cutouts 271-276 is disposed between adjacent cutouts 191-194 ofthe first pixel electrode 190 a, or between the cutout 191 and achamfered edge of the second pixel electrode 190 b. In addition, each ofthe cutouts 271-276 has at least an oblique portion extending parallelto the upper cutout 192 or the lower cutout 192 of the first pixelelectrode 190 a, and the distances between adjacent two of the cutouts271-276 and 191-194, the oblique portions thereof, and the chamferededges of the second pixel electrode 190 b, which are parallel to eachother, are substantially the same. The cutouts 271-276 substantiallyhave inversion symmetry with respect to an imaginary transverse centerline of the first pixel electrode 190 a. The oblique portions of thecutouts 271, 272 and 276 overlap the oblique portions of the couplingelectrodes 176 b that prevents light leakage near the cutouts 271, 272and 276.

Each of the cutouts 271 and 276 has an oblique portion extendingapproximately from a left edge of the pixel electrode 190 approximatelyto an upper or lower edge of the pixel electrode 190 and transverse andlongitudinal portions extending from respective ends of the obliqueportion along edges of the pixel electrode 190, overlapping the edges ofthe pixel electrode 190, and making obtuse angles with the obliqueportion.

Each of the cutouts 272 and 275 has an oblique portion, a longitudinalportion connected to an end of the oblique portion, and an expansionconnected to the other end of the oblique portion. The oblique portionextends approximately from the left edge of the pixel electrode 190approximately to upper right or lower right corner of the pixelelectrode 190. The longitudinal portion extends from the end of theoblique portion along the left edge of the pixel electrode 190, overlapsthe left edge of the pixel electrode 190, and makes an obtuse angle withthe oblique portion. The expansion covers the respective corner of thepixel electrode 190.

The cutout 273 has a pair of oblique portions extending approximatelyfrom the center of the left edge of the pixel electrode 190 to the rightedge of the pixel electrode 190, a transverse portion extending from ameeting point of the oblique portions to the left, and a pair oflongitudinal portions extending from the respective oblique portionsalong the right edge of the pixel electrode 190, overlapping the rightedge of the pixel electrode 190, and making an obtuse angle with therespective oblique portions. The cutout 274 has a transverse portionextending along the transverse center line of the pixel electrode 190, apair of oblique portions extending from the transverse portionapproximately to the right edge of the pixel electrode 190 and makingobtuse angles with the transverse portion, and a pair of longitudinalportions extending from the respective oblique portions along the rightedge of the pixel electrode 190, overlapping the right edge of the pixelelectrode 190, and making an obtuse angle with the respective obliqueportions.

The number of the cutouts 271-276 may be varied depending on the designfactors, and the light blocking member 220 may also overlap the cutouts271-276 to block the light leakage through the cutouts 271-276.

In the meantime, the cutouts 271-276 may expose portions of the colorfilters 230 if there is no overcoat 250, and the exposed portions of thecolor filters 230 may contaminate the LC layer 300.

Alignment layers 11 and 21 for aligning the LC molecules 310 are coatedon inner surfaces of the panels 100 and 200, and crossed polarizers 12and 22 are provided on outer surfaces of the panels 100 and 200,respectively, such that a transmissive axis of one of the polarizers 12and 22 is parallel to the transverse direction. One of the polarizersmay be omitted when the LCD is a reflective LCD.

The LC layer 300 has negative dielectric anisotropy and the LC molecules310 in the LC layer 300 are aligned such that their long axes aresubstantially vertical to the surfaces of the panels in absence ofelectric field.

The LCD shown in FIGS. 1-4 is represented as an equivalent circuit shownin FIG. 5.

Referring to FIG. 5, the LCD includes a plurality of gate lines, aplurality of data lines, and a plurality of pixels and each pixelincludes a pair of first and second subpixels and a coupling capacitorCcpb. Each subpixel includes a first/second LC capacitor Clca/Clcb, afirst/second storage electrode Csta/Cstb, and a first/second TFT T1/T2.The first/second LC capacitor Clca/Clcb is formed of a first/secondpixel electrode 190 a/190 b, a common electrode 270, and a region of aLC layer 300 disposed on the first/second pixel electrode 190 a/190 b.The first/second storage capacitor Csta/Cstb is formed of thefirst/second pixel electrode 190 a/190 b, a storage electrode line 131,and insulator(s) 140 and 180 interposed therebetween. The first TFT T1is connected to a gate line, a data line supplied with data voltages,and the capacitor Clca and Csta, while the second TFT T2 is connected toa gate line previous to the gate line connected to the TFT T1, a storageelectrode line supplied with a common voltage, and the capacitors Clcband Cstb. The coupling capacitor Ccpb is formed of a coupling electrode176 b, the second pixel electrode 190 b, and an insulator 140 interposedtherebetween, and connected between output terminals of the TFTs T1 andT2.

Now, a behavior of a pixel is described in detail.

When the previous gate line connected to the second TFT T2 is suppliedwith a gate-on voltage, the second TFT T2 turns on to transmit thecommon voltage to the second pixel electrode 190 b, which in turn isrefreshed by the common voltage. When the previous gate line is suppliedwith a gate-off voltage, the second pixel electrode 190 b becomesfloating. When the current gate line connected to the first TFT T1 issupplied with a gate-on voltage, the first TFT T1 turns on to transmit adata voltage to the first pixel electrode 190 a. Since the second pixelelectrode 190 b is floating and capacitively coupled to the first pixelelectrode 190 a through the coupling capacitor Ccpb, the voltage of thesecond pixel electrode 190 b is changed the capacitive coupling. Thecapacitive coupling makes the magnitude of the voltage of the secondpixel electrode 190 b higher than that of the first pixel electrode 190a, which will be described in detail.

The voltage across the first LC capacitor Clca is denoted by Va(=Vd1),and the voltage across the second LC capacitor Clcb is denoted by Vb.The voltage distribution law results in:Vb≈1/(C₁+2C₂)×[(2−C₃/C₂)×(C₁+C₂)×Vd1],where C₁=Clca+Csta, C₂=Ccpb, and C₃=Clcb+Cstb, and capacitances of thecapacitors Clca, Csta, Clcb, Cstb, and Ccpb are denoted by the samecharacters as those of the capacitors Clca, Csta, Clcb, Cstb, and Ccpb.Parasitic capacitances between terminals of the TFTs T1 and T2 areneglected since it is trivial.

The voltage Vb can be controlled such that the voltage Vb approaches thevoltage Va but always higher than the voltage Va by adjusting thecapacitances capacitors Clca, Csta, Clcb, Cstb, and Ccpb. In particular,the ratio of the voltages Va and Vb can be effectively controlled byadjusting the capacitance Ccpb. The capacitance Ccpb can be adjusted byvarying the overlapping area or the distance between the couplingelectrode 176 b and the second pixel electrode 190 b. For example, theoverlapping area can be varied by changing the width of the couplingelectrode 176 b and the distance can be varied by placing the couplingelectrode 176 b in the same layer as the gate lines 121.

The non-zero voltages across the LC capacitors Clca and Clcb generateelectric fields substantially perpendicular to the surfaces of thepanels 100 and 200 and the LC molecules 310 tend to change theirorientations in response to the electric field such that their long axesare perpendicular to the field directions. Since the field strength inthe first LC capacitor Clca is different from that in the second LCcapacitor Clcb, the LC molecules 310 in the first and the second LCcapacitors Clca and Clcb experience different tilting forces to havedifferent tilt angles. Accordingly, the lateral visibility is improved.

According to experiments, the lateral visibility of LCDs according tothis embodiment represented by 1−(gradient of lateral gammacurve)/(gradient of front gamma curve) was measured to be about0.22-0.35 that is excellent. In addition, the aperture ratio of the LCDswas almost equal to that of LCDs having a pixel electrode per a pixel.

The area of the first pixel electrode 190 a is preferably larger thanthat of the second pixel electrode 190 b, but it is preferably smallerthan about six times the area of the second pixel electrode 190 b. Inthe LCD shown in FIGS. 1-4, the area of the first pixel electrode 190 ais about five times the area of the second pixel electrode 190 b. Inaddition, the ratio of the voltages Va and Vb is preferably in a rangebetween about 0.50 and about 0.95.

In the meantime, a set of the cutouts 191-194 and 271-276 divides a pairof first and second pixel electrodes 190 a and 190 b into a plurality ofsubareas and each subarea has two major edges as shown in FIG. 3. Thecutouts 191-194 and 271-276 control the tilt directions of the LCmolecules 310 in the LC layer 300. This will be described in detail.

The cutouts 191-194 and 271-276 of the first electrodes 190 a and 270and the edges of the second pixel electrodes 190 distort the electricfields to have a horizontal component. The horizontal components of theelectric fields are perpendicular to the edges of the cutouts 191-194and 271-276 and the edges of the pixel electrodes 190.

Accordingly, the tilt directions of the LC molecules 310 on the subareasare different and thus the viewing angle is enlarged.

At least one of the cutouts 191-194 and 271-276 can be substituted withprotrusions or depressions, and the shapes and the arrangements of thecutouts 191-194 and 271-276 may be modified.

Furthermore, and the shape and the position of the coupling electrode176 b may be modified, which will be described in detail.

An LCD according to another embodiment of the present invention will bedescribed in detail with reference to FIGS. 6 and 7.

FIG. 6 is a layout view of a TFT array panel for an LCD according toanother embodiment of the present invention, and FIG. 7 is an equivalentcircuit diagram of an LCD including the TFT array panel shown in FIG. 6.

An LCD according to this embodiment includes a TFT array panel shown inFIG. 6, the common electrode panel 200 shown in FIG. 2, and the LC layer310 shown in FIG. 4, and layered structures of the panels according tothis embodiment are almost the same as that shown in FIG. 4.

Regarding the TFT array panel, a plurality of gate lines 121 including aplurality of first and second gate electrodes 123 a and 123 b and endportions 125 and a plurality of storage electrode lines 131 including aplurality of first to third storage electrodes 133 a-133 c and branchconnections 133 d are formed on a substrate 110, and a gate insulatinglayer 140, a plurality of semiconductor stripes 151 including aplurality of projections 154 a and a plurality of semiconductor islands154 b, and a plurality of ohmic contact stripes 161 including aplurality of projections 163 and a plurality of ohmic contact islands165 are sequentially formed thereon. A plurality of data lines 171including a plurality of first source electrodes 173 a and end portions179, and a plurality of first and second drain electrodes 175 a and 175b are formed on the ohmic contacts 161 and 165, and a passivation layer180 is formed thereon. A plurality of contact holes 181 a-186 areprovided at the passivation layer 180 and the gate insulating layer 140.A plurality of sets of first and second pixel electrodes 190 a and 190 bhaving a plurality of cutouts 191-194, a plurality of contact assistants95 and 97, and a plurality of storage connections 91 are formed on thepassivation layer 180.

Regarding the common electrode panel 200, a light blocking member 220, aplurality of color filters 230, an overcoat 250, and a common electrode270 having a plurality of cutouts 271-276 are formed on an insulatingsubstrate 210 as shown in FIGS. 2 and 4.

Different from the LCD shown in FIGS. 1-5, a pair of first and secondpixel electrodes 190 a and 190 b according to this embodiment aredivided along a cutout 192 rather than a cutout 191 and a pixel of theLCD according to this embodiment includes first to third TFTs T1-T3.Like the LCD shown in FIGS. 1-5, the first TFT T1 is connected to a gateline, a data line supplied with data voltages, and a first LC capacitorClca and a first storage capacitor Csta, while the second TFT T2 isconnected to a gate line previous to the gate line connected to the TFTT1, a storage electrode line supplied with a common voltage, and asecond LC capacitor Clcb and a second storage capacitor Cstb. The thirdTFT T3 is connected to the previous gate line, the data line, and thecapacitors Clcb and Cstb.

Referring to FIG. 6, the first TFT T1 includes a first gate electrode123 a, a first source electrode 173 a, and a first drain electrode 175a, while the third TFT T3 includes a first gate electrode 123 aconnected to the previous gate line, a first source electrode 173 a, anda third drain electrode 175 c. The second TFT T2 includes a second gateelectrode 123 b, a second source electrode 173 b, and a second drainelectrode 175 b.

The first and the third drain electrodes 175 a and 175 extend along asecond storage electrode 133 b and then they are curved along a cutout274 to meet each other. The first drain electrode 175 a has a pair ofbranches that form a coupling electrode 176 b and overlap the cutouts271 and 272. The third drain electrode 175 d has a branch that forms acoupling electrode 176 c and overlaps the cutout 275.

In operation, when the previous gate line connected to the second andthe third TFTs T2 and T3 is supplied with a gate-on voltage, the secondTFT T2 turns on to transmit the common voltage to the second pixelelectrode 190 b and the third TFT T3 also turns on to transmit a datavoltage for a previous pixel to the first pixel electrode 190 a. Then,the coupling capacitor Ccpb stores the voltage difference between theprevious data voltage and the common voltage. When the current gate lineconnected to the first TFT T1 is supplied with a gate-on voltage, thefirst TFT T1 turns on to transmit a data voltage for a current pixel tothe first pixel electrode 190 a. Since the second pixel electrode 190 bis floating and capacitively coupled to the first pixel electrode 190 athrough the coupling capacitor Ccpb, the voltage of the second pixelelectrode 190 b is changed by the capacitive coupling.

Many of the above-described features of the LCD shown in FIGS. 1-5 maybe appropriate to the LCD shown in FIGS. 6 and 7.

An LCD according to another embodiment of the present invention will bedescribed in detail with reference to FIGS. 8 and 9.

FIG. 8 is a layout view of a TFT array panel for an LCD according toanother embodiment of the present invention, and FIG. 9 is an equivalentcircuit diagram of an LCD including the TFT array panel shown in FIG. 8.

An LCD according to this embodiment includes a TFT array panel shown inFIG. 8, the common electrode panel 200 shown in FIG. 2, and the LC layer310 shown in FIG. 4, and layered structures of the panels according tothis embodiment are almost the same as that shown in FIG. 4.

Regarding the TFT array panel that is similar to that shown in FIG. 6, aplurality of gate lines 121 including a plurality of first and secondgate electrodes 123 a and 123 b and end portions 125 and a plurality ofstorage electrode lines 131 including a plurality of first to thirdstorage electrodes 133 a-133 c and branch connections 133 d are formedon a substrate 110, and a gate insulating layer 140, a plurality ofsemiconductor stripes 151 including a plurality of projections 154 a anda plurality of semiconductor islands 154 b, and a plurality of ohmiccontact stripes 161 including a plurality of projections 163 and aplurality of ohmic contact islands 165 are sequentially formed thereon.A plurality of data lines 171 including a plurality of first sourceelectrodes 173 a and end portions 179, and a plurality of first andsecond drain electrodes 175 a and 175 b are formed on the ohmic contacts161 and 165, and a passivation layer 180 is formed thereon. A pluralityof contact holes 181 a-186 are provided at the passivation layer 180 andthe gate insulating layer 140. A plurality of sets of pixel electrodes190 a-190 c having a plurality of cutouts 191-194, a plurality ofcontact assistants 95 and 97, and a plurality of storage connections 91are formed on the passivation layer 180.

Regarding the common electrode panel 200, a light blocking member 220, aplurality of color filters 230, an overcoat 250, and a common electrode270 having a plurality of cutouts 271-276 are formed on an insulatingsubstrate 210 as shown in FIGS. 2 and 4.

Different from the LCD shown in FIGS. 6 and 7, a set of pixel electrodes190 a-190 c include first, second and a pair of third pixel electrodes190 a-190 c forming first to third LC capacitors Clca, Clcb and Clcb andfirst to third storage capacitors Csta, Cstb and Cstc. The first and thesecond pixel electrodes 190 a and 190 b are divided along a cutout 192,while the second and the third pixel electrodes 190 b and 190 c aredivided along a cutout 191. The third electrodes 190 c are floating.

In addition, the first drain electrode 175 a has a branch that form acoupling electrode 176 b and includes a transverse portion overlapping athird storage electrode 133 c, an oblique portion connected to thetransverse portion and overlapping a cutout 271, a longitudinal portionoverlapping a storage electrode 13 a, and a pair of oblique portionspartly overlapping cutouts 275 and 276. Accordingly, the couplingelectrode 176 b overlaps the second and the third pixel electrodes 190 band 190 c to form coupling capacitors Ccpb and Ccpc. The third drainelectrode 175 d has no branch.

In operation, when the previous gate line connected to the second andthe third TFTs T2 and T3 is supplied with a gate-on voltage, the secondTFT T2 turns on to transmit the common voltage to the second pixelelectrode 190 b and the third TFT T3 also turns on to transmit a datavoltage for a previous pixel to the first pixel electrode 190 a. Whenthe current gate line connected to the first TFT T1 is supplied with agate-on voltage, the first TFT T1 turns on to transmit a data voltagefor a current pixel to the first pixel electrode 190 a. Since the secondand the third pixel electrodes 190 b and 190 c are floating andcapacitively coupled to the first pixel electrode 190 a through thecoupling capacitor Ccpb, the voltages of the second and the third pixelelectrodes 190 b and 190 c are changed by the capacitive coupling. Thecapacitive coupling makes the magnitude of the voltage of the secondpixel electrode 190 b higher than that of the first pixel electrode 190a, and it makes the magnitude of the voltage of the third pixelelectrode 190 c lower than that of the first pixel electrode 190 a,which will be described in detail.

The voltage across the first LC capacitor Clca is denoted by Va, and thevoltage across the third LC capacitor Clcc is denoted by Vc. The voltagedistribution law results in:Vb≈Va×[(Ccpc/(Ccpc+Clcc)]<Va,where capacitances of the capacitors Clcpc and Clcc are denoted by thesame characters as those of the capacitors Clcpc and Clcc. The ratio ofthe voltages Va and Vc can be effectively controlled by adjusting thecapacitance Ccpc. The capacitance Ccpc can be adjusted by varying theoverlapping area or the distance between the coupling electrode 176 band the third pixel electrode 190 c. In the LCD shown in FIGS. 1-4, thearea of the first to the third pixel electrode 190 a has a proportionrelation 1:1.37:0.44.

Many of the above-described features of the LCD shown in FIGS. 1-7 maybe appropriate to the LCD shown in FIGS. 8 and 9.

An LCD according to another embodiment of the present invention will bedescribed in detail with reference to FIGS. 10 and 11.

FIG. 10 is a layout view of a TFT array panel for an LCD according toanother embodiment of the present invention, and FIG. 11 is anequivalent circuit diagram of an LCD including the TFT array panel shownin FIG. 10.

An LCD according to this embodiment includes a TFT array panel shown inFIG. 10, the common electrode panel 200 shown in FIG. 2, and the LClayer 310 shown in FIG. 4, and layered structures of the panelsaccording to this embodiment are almost the same as that shown in FIG.4.

Regarding the TFT array panel, a plurality of gate lines 121 including aplurality of first and second gate electrodes 123 a and 123 b and endportions 125 and a plurality of storage electrode lines 131 including aplurality of first to third storage electrodes 133 a-133 c and branchconnections 133 d are formed on a substrate 110, and a gate insulatinglayer 140, a plurality of semiconductor stripes 151 including aplurality of projections 154 a and a plurality of semiconductor islands154 b, and a plurality of ohmic contact stripes 161 including aplurality of projections 163 and a plurality of ohmic contact islands165 are sequentially formed thereon. A plurality of data lines 171including a plurality of first source electrodes 173 a and end portions179, and a plurality of first and second drain electrodes 175 a and 175b are formed on the ohmic contacts 161 and 165, and a passivation layer180 is formed thereon. A plurality of contact holes 181 a and 182-186are provided at the passivation layer 180 and the gate insulating layer140. A plurality of sets of first and second pixel electrodes 190 a and190 b having a plurality of cutouts 191-194, a plurality of contactassistants 95 and 97, and a plurality of storage connections 91 areformed on the passivation layer 180.

Regarding the common electrode panel 200, a light blocking member 220, aplurality of color filters 230, an overcoat 250, and a common electrode270 having a plurality of cutouts 271-276 are formed on an insulatingsubstrate 210 as shown in FIGS. 2 and 4.

Different from the LCD shown in FIGS. 1-5, the second pixel electrodes190 b according to this embodiment are floating and there is no contacthole exposing the first drain electrode 175 a. In addition, the couplingelectrodes 176 a overlap all the cutouts 271-276 and almost all thestorage electrodes 133 a-133 c. Accordingly, the coupling electrode 176b overlaps the first and the second pixel electrodes 190 a and 190 b toform coupling capacitors Ccpa and Ccpb. The capacitive coupling makesthe magnitude of the magnitude of the voltage of the second pixelelectrode 190 c lower than that of the first pixel electrode 190 a.

Many of the above-described features of the LCD shown in FIGS. 1-5 maybe appropriate to the LCD shown in FIGS. 10 and 11.

An LCD according to another embodiment of the present invention will bedescribed in detail with reference to FIGS. 12 and 13.

FIGS. 12 and 13 are layout views of TFT array panels for an LCDaccording to another embodiment of the present invention.

Each LCD according to these embodiments includes a TFT array panel shownin FIG. 12 or 13, the common electrode panel 200 shown in FIG. 2, andthe LC layer 310 shown in FIG. 4, and layered structures of the panelsaccording to this embodiment are almost the same as that shown in FIG.4.

Regarding the TFT array panel, a plurality of gate lines 121 including aplurality of first and second gate electrodes 123 a and 123 b and endportions 125 and a plurality of storage electrode lines 131 including aplurality of first to third storage electrodes 133 a-133 c and branchconnections 133 d are formed on a substrate 110, and a gate insulatinglayer 140, a plurality of semiconductor stripes 151 including aplurality of projections 154 a and a plurality of semiconductor islands154 b, and a plurality of ohmic contact stripes 161 including aplurality of projections 163 and a plurality of ohmic contact islands165 are sequentially formed thereon. A plurality of data lines 171including a plurality of first source electrodes 173 a and end portions179, and a plurality of first and second drain electrodes 175 a and 175b are formed on the ohmic contacts 161 and 165, and a passivation layer180 is formed thereon. A plurality of contact holes 181 a-186 areprovided at the passivation layer 180 and the gate insulating layer 140.A plurality of sets of first and second pixel electrodes 190 a and 190 bhaving a plurality of cutouts 191-194, a plurality of contact assistants95 and 97, and a plurality of storage connections 91 are formed on thepassivation layer 180. The areal ratio of the first and the second pixelelectrodes 190 a and 190 b is about 5:1.

Regarding the common electrode panel 200, a light blocking member 220, aplurality of color filters 230, an overcoat 250, and a common electrode270 having a plurality of cutouts 271-276 are formed on an insulatingsubstrate 210 as shown in FIGS. 2 and 4.

The LCD shown in FIG. 12 has a similar layout to the LCD shown in FIG.6. However, a pair of first and second pixel electrodes 190 a and 190 bare divided along a cutout 191 rather than a cutout 192. In addition, acoupling electrode 176 b extending from the first drain electrode 175 ahas a transverse portion overlapping the third storage electrode,oblique portions overlapping the cutouts 271 and 272, and a longitudinalportion overlapping the first storage electrode 133 a.

The LCD shown in FIG. 13 has a similar layout as the LCD shown in FIG.10. However, a coupling electrode 176 b extending from the drainelectrode 175 a and 175 b has less overlapping portions than that shownin FIG. 10. For example, a longitudinal portion overlapping the firststorage electrode 133 a is shorter than that shown in FIG. 10.

Many of the above-described features of the LCD shown in FIGS. 1-5, 6and 10 may be appropriate to the LCD shown in FIGS. 12 and 13.

While the present invention has been described in detail with referenceto the preferred embodiments, those skilled in the art will appreciatethat various modifications and substitutions can be made thereto withoutdeparting from the spirit and scope of the present invention as setforth in the appended claims.

What is claimed is:
 1. A liquid crystal display comprising: a firstsubstrate; a plurality of first signal lines formed on the firstsubstrate; a plurality of second signal lines intersecting the firstsignal lines; a first pixel electrode and a second pixel electrodedisposed in a pixel area and having different areas from each other; afirst thin film transistor connected to the first pixel electrode; asecond thin film transistor connected to the second pixel electrode; asecond substrate facing the first substrate; and a liquid crystal layerinterposed between the first and second substrates and including liquidcrystal molecules, wherein the liquid crystal molecules are oriented bya plurality of tilt direction defining members when an electric field isapplied to the first pixel electrode or the second pixel electrode, andwherein the oriented directions of the liquid crystal molecules areinclined with respect to the first signal lines or the second signallines and are different.
 2. The liquid crystal display of claim 1,wherein the first pixel electrode has an area smaller than the secondpixel electrode.
 3. The liquid crystal display of claim 2, wherein thearea of second pixel electrode is about 1-5 times larger than the areaof the first pixel electrode.
 4. The liquid crystal display of claim 1,wherein the first pixel electrode is supplied with higher voltage thanthe second pixel electrode.
 5. The liquid crystal display of claim 4,further comprising a common electrode formed on the second substrate,wherein a ratio of a voltage difference between the first pixelelectrode and the common electrode and a voltage difference between thesecond pixel electrode and the common electrode is in a range betweenabout 0.5-0.95.
 6. The liquid crystal display of claim 1, wherein thefirst and the second pixel electrodes are capacitively coupled to eachother.
 7. The liquid crystal display of claim 1, further comprising athird pixel electrode separated from the first and the second pixelelectrodes.
 8. The liquid crystal display of claim 7, wherein areas ofthe first, the second, and the third pixel electrodes are different fromeach other.
 9. The liquid crystal display of claim 7, wherein the thirdpixel electrode is capacitively coupled to the second pixel electrode.10. The liquid crystal display of claim 7, wherein a ratio of the areasof the first, the second, and the third pixel electrodes is about1.37:1:0.44.
 11. The liquid crystal display of claim 1, wherein thefirst pixel electrode or the second pixel electrode has a tilt directiondefining member.
 12. The liquid crystal display of claim 11, wherein thetilt direction defining member is a cutout.
 13. The liquid crystaldisplay of claim 1, further comprising a storage electrode lineconnected to the first thin film transistor.